Add sourcelink to enable source debugging of the nuget package (#4)

Add sourcelink to enable source debugging of the nuget package

Remove SonarQube analysis from build
- I've tried hard with SonarQube, but its just too annoying to use

Fix the code coverage in the build. There were two problems, 
- "nuget restore" wasn't working properly, so switched to dotnet restore
- I had to use `-register:Path64` argument for opencover. I'm not sure why, as `-register:User` used to work, and is supposed to do so without admin permissions.

Author: ceddlyburge

README.md

@@ -4,8 +4,6 @@ A C# library for strongly typed Configuration with validation
 
 [![Build status](https://ci.appveyor.com/api/projects/status/oujy1v19iwdba8e5?svg=true)](https://ci.appveyor.com/project/RESSoftwareTeam/configuration)
 
-[![Quality gate](https://sonarcloud.io/api/project_badges/quality_gate?project=res.configuration)](https://sonarcloud.io/dashboard?id=res.configuration)
-
 [![codecov](https://codecov.io/gh/resgroup/configuration/branch/master/graph/badge.svg)](https://codecov.io/gh/resgroup/configuration)
 
 Example Usage (`Configuration` is the class provided by this repo)

RES.Configuration.Test/RES.Configuration.Test.csproj

@@ -11,10 +11,10 @@
         <AppendRuntimeIdentifierToOutputPath>false</AppendRuntimeIdentifierToOutputPath>
         <BaseOutputPath>..\BuiltDLLs\</BaseOutputPath>
         <ProjectGuid>40b5b4a7-ad9a-4cec-b1cf-059482dfb9ce</ProjectGuid>
-        <!-- only required for sonar qube, and only until they fix a .net core type issue https://jira.sonarsource.com/browse/SONARMSBRU-167 -->
     </PropertyGroup>
-    <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|AnyCPU'">
+    <PropertyGroup>
         <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+        <DebugSymbols>True</DebugSymbols>
         <WarningsAsErrors />
         <NoWarn>1701;1702;1705;1125</NoWarn>
     </PropertyGroup>